KENNARD : HOLOCENE NON-MARINE MOLLUSCA OF ENGLAND. 255 



it is essential to have large series of specimens, for giants and dwarfs 

 are not uncommon, and the contrasted series must be from the same 

 geological formation. It would be misleading to compare fossil 

 shells that had lived on the Chalk and recent shells collected on 

 the Gault. Exigencies of space prevent me from giving the numerous 

 measurements, and after all the results are the important matter, 

 and these show that in many deposits, some of which can be dated 

 archseologically, the average size of the mollusca is decidedly larger 

 than the mean of those now living in the immediate neighbourhood. 

 The cause of this is in my opinion changed meteorological conditions. 



If we compare the non-marine mollusca of South Devonshire 

 and Kent, differences in the size will be noted. The former 

 possesses what is known as an insular type of climate, but little 

 frost and absence of extreme heat in summer, whereas Kent 

 approaches to the continental type with hotter summers and colder 

 winters. 



Xerophiles such as Jacosta {Cernuella) virgata (Da Cost.), 

 J, (Xerophila) itala (Linn.), and J. (Candidula) caperata (Mont.) 

 are far more abundant and larger in Kent than in South Devon, 

 whilst Helix aspersa, Miill., attains a larger size in the former 

 county. 



Devon examples of Helix nemoralis, Linn., are perhaps brighter 

 coloured, a character of no value to the palaeontologist, but are 

 certainly smaller than Kentish specimens. The chief difference, 

 however, is the comparative abundance of heavy shells in South 

 Devon compared with their extreme rarity in Kent. This no doubt 

 arises from the mild winters being favourable to longevity, a fact 

 which has long been known to Harley Street specialists. Kentish 

 examples of Arianta arbustorum (Linn.) and Fniticicola (Capillifera) 

 striolata (C. Pfr.) are decidedly larger than those from Devon, and this 

 remark applies to many of the land and freshwater forms. When 

 we compare English examples with foreign similar differences are 

 noted. With HeMx aspersa, Miill., the largest examples are from 

 Algiers and Greece, whilst shells from Beyrout, Italy, Spain, and 

 Majorca are not far behind. Shells from Crete, Tasmania, 

 Melbourne, and Mauritius are about an English average, whilst 

 those from Cape Town and the Canaries are slightly smaller. These 

 are larger than examples from Portugal and Costa Rica, whilst the 

 smallest are from St. Helena, the Seychelles, and Lord Howes 

 Island. From these facts one may infer that a " continental " 

 climate is more favourable to this species than an " insular ". 



The largest examples of Helix nemoralis, Linn., are found in 

 Lombardy, the Pyrenees, Portugal, Switzerland, and in Ireland in 

 Co. Clare and the Aran Islands, West Galway ; whilst French and 

 German examples are certainly larger than EngUsh. 



Now these facts do not 8.gree with the data for Helix aspersa, 

 Linn., for the Irish examples of H. nemoralis are an apparent 

 exception, but the Irish localities are exceptionally arid, being 



